Shining a Light on Kauai's Buried Treasure

By Wendy Kishida and Michelle Clark

A Kaua'i cave wolf spider with spiderlings on its back. The spider was discovered in 1973 and is only know to occur in a few caves in the Koloa-Poipu region.

Photo Credit: Wendy Kishida

In the dark zones of a few inhospitable caves on Hawaii's Kauai Island, a truly unique story of predator and prey plays out. The endangered Kauai cave wolf spider (Adelocosa anops) feeds on the equally endangered Kauai cave amphipod (Spelaeorchestia koloana). These cave adapted creatures were among the first animals to arrive and evolve on Kauai around 5 million years ago.

Both the spider and amphipod gained federal protection in January 2000. Threats to these species include urban and agricultural development above the cave and lava flow footprints; non-native species preying upon them or competing with them for limited food resources; pollution; human visitation to the caves; and extended drought, which can reduce the high humidity environment that the species are adapted to.

The spider, which grows to the size of a fifty cent piece, is restricted to only a handful of caves in the Koloa District of Kauai. Locals know the harmless spider – covered with beautiful golden bronze hairs – as pe'e pe'e maka'ole. While wolf spiders in general are known for their sharp eyesight, the Kauai wolf spider is eyeless, relying exclusively on touch—its sensitive hairs allow it to track prey. The top predator of these caves, the spider waits with its front two legs raised in the air, then strikes passing amphipods with incredible force and accuracy.

The Kaua'i cave amphipod feeds on the decaying roots of surface vegetation that reach into the cave system, as well as rotting sticks, branches, and other plant materials.

Photo Credit: Wendy Kishida

The Kauai cave amphipod, known locally as 'uku noho ana, resembles a shrimp with translucent white coloring—a common adaptation for those animals dwelling in perpetual darkness. While amphipods above-ground move by jumping, the cave amphipod creeps slowly along cave walls, eating dead roots and organic material. It will jump if provoked, but the cave amphipod's blindness makes jumping in its cave environment perilous; jumping is a last resort to navigate the cave and evade predators.

These species thrive in cave environments, where the temperature remains near 77 degrees Fahrenheit (25 degrees Celsius), the surroundings are wet, and the air is humid and rich with carbon dioxide. Most of the caves where these animals persist are lava tubes, except for a single limestone cave that sits on top of the same lava flow comprising the other caves.

Twice annually U.S. Fish and Wildlife Service (Service) biologists survey Kauai's caves for these creatures—a tedious and difficult task. Many caves have large footprints with tight entrances and low ceilings. Gloves, knee pads, hard hats, and headlamps are musts for biologists as they crawl through the caves—each movement taken with great care as not to crush the animals they are searching for. Spotting these endangered creatures makes the long journey through these inhospitable caves worth it; they shine like jewels under the light of the headlamp and invoke a sense of reverence and awe.

Surveys have shown fluctuations in both the amphipod and spider numbers over time, but since these cryptic species spend the majority of their lives in voids and cracks inaccessible to humans, basic information, such as population size, remains unknown.

The Service, with support from the Natural Resource Conservation Service and private landowners, works to conserve these unique species and restore habitat. Partners have secured cave entry sites and planted native vegetation – such as the native Hawaiian caper (Capparis sandwichiana) and other species with extensive root systems – in areas above the caves. The roots of the Hawaiian caper penetrate the caves and provide food for the amphipod. DNA analysis is bettering biologists' knowledge of which plants send roots into the caves. This analysis — a collaborative effort between Saint Mary's College in Moraga California and the University of California-Berkeley – will help biologists better understand if habitat restoration efforts above the cave are having the desired effect within the cave.

Since 2004, private landowners – with support from the Hawaii Plant Extinction Prevention Program, the University of Hawaii, and the Bishop Museum – have played a significant role in enhancing habitat for the cave species. Old sugar cane fields above the caves were restored to native shrub land and the caves entrances were blocked to reduce airflow. Climatic parameters of relative humidity, cave air temperature, cave soil temperature, and cave soil water content were measured over time and compared to that of caves where the cave species occurred naturally. This research revealed that relative humidity is a key factor in restoring caves. Efforts to restore and create habitat have paid off—the species were recently discovered in four caves where they were not previously found.

The Service is currently working with a private landowner to set aside three preserves totaling 34 acres (14 hectares) to benefit these cave animals. The preserve, coupled with the management plan, brings hope for the continuity of Kauai's rare underground treasures.

Wendy Kishida is the Kauai Coordinator for the Hawaii Plant Extinction Prevention Program. Michelle Clark, a Kauai partnerships biologist in the Service's Pacific Islands Fish and Wildlife Office, can be reached at michelle_clark@fws.gov or 808-822-4315.